Light emitting device and plant cultivation method

ABSTRACT

Provided is a light emitting device that includes a light emitting element having a light emission peak wavelength ranging from 380 nm to 490 nm, and a fluorescent material excited by light from the light emitting element and emitting light having at a light emission peak wavelength ranging from 580 nm or more to less than 680 nm. The light emitting device emits light having a ratio R/B of a photon flux density R to a photon flux density B ranging from 2.0 to 4.0 and a ratio R/FR of the photon flux density R to a photon flux density FR ranging from 0.7 to 13.0, the photon flux density R being in a wavelength range of 620 nm or more and less than 700 nm, the photon flux density B being in a wavelength range of 380 nm or more and 490 nm or less, and the photon flux density FR being in a wavelength range of 700 nm or more and 780 nm or less.

CROSS-REFERENCE TO RELATED APPLICATION

This is a continuation application of U.S. patent application Ser. No.15/634,401, filed Jun. 27, 2017, which claims benefit of Japanese PatentApplication No. 2016-128835 filed on Jun. 29, 2016, the entiredisclosure of which are hereby incorporated by reference in theirentirety.

BACKGROUND Technical Field

The present disclosure relates to a light emitting device and a plantcultivation method.

Description of Related Art

With environmental changes due to climate change and other artificialdisruptions, plant factories are expected to increase productionefficiency of vegetables and be capable of adjusting production in orderto make it possible to stably supply vegetables. Plant factories thatare capable of artificial management can stably supply clean and safevegetables to markets, and therefore are expected to be thenext-generation industries.

Plant factories that are completely isolated from external environmentmake it possible to artificially control and collect various data suchas growth method, growth rate data, yield data, depending onclassification of plants. Based on those data, plant factories are ableto plan production according to the balance between supply and demand inmarkets, and supply plants such as vegetables without depending onsurrounding conditions such as climatic environment. Particularly, anincrease in food production is indispensable with world populationgrowth. If plants can be systematically produced without the influenceby surrounding conditions such as climatic environment, vegetablesproduced in plant factories can be stably supplied within a country, andadditionally can be exported abroad as viable products.

In general, vegetables that are grown outdoors get sunlight, grow whileconducting photosynthesis, and are gathered. On the other hand,vegetables that are grown in plant factories are required to beharvested in a short period of time, or are required to grow in largerthan normal sizes even in an ordinary growth period.

In plant factories, the light source used in place of sunlight affect agrowth period, growth of plants. LED lighting is being used in place ofconventional fluorescent lamps, from a standpoint of power consumptionreduction.

For example, Japanese Unexamined Patent Publication No. 2009-125007discloses a plant growth method. In this method, the plants isirradiated with light emitted from a first LED light emitting elementand/or a second LED light emitting element at predetermined timingsusing a lighting apparatus including the first LED light emittingelement emitting light having a wavelength region of 625 to 690 nm andthe second LED light emitting element emitting light having a wavelengthregion of 420 to 490 nm in order to emit lights having sufficientintensities and different wavelengths from each other.

SUMMARY

However, even though plants are merely irradiated with lights havingdifferent wavelengths as in the plant growth method disclosed inJapanese Unexamined Patent Publication No. 2009-125007, the effect ofpromoting plant growth is not sufficient. Further improvement isrequired in promotion of plant growth.

Accordingly, an object of the present disclosure is to provide a lightemitting device capable of promoting growth of plants and a plantcultivation method.

Means for solving the above problems are as follows, and the presentdisclosure includes the following embodiments.

A first embodiment of the present disclosure is a light emitting deviceincluding a light emitting element having a light emission peakwavelength in a range of 380 nm or more and 490 nm or less, and afluorescent material that is excited by light from the light emittingelement and emits light having at least one light emission peakwavelength in a range of 580 nm or more and less than 680 nm. The lightemitting device emits light having a ratio R/B of a photon flux densityR to a photon flux density B within a range of 2.0 or more and 4.0 orless, and a ratio R/FR of a photon flux density R to a photon fluxdensity FR within a range of 0.7 or more and 13.0 or less, where thephoton flux density R is the number of light quanta (μmol·m⁻²·g⁻¹)incident per unit time and unit area in a wavelength range of 620 nm ormore and less than 700 nm, the photon flux density B is the number oflight quanta (μmol·m⁻²·g⁻¹) incident per unit time and unit area in awavelength range of 380 nm or more and 490 nm or less, and the photonflux density FR is the number of light quanta (μmol ·m⁻²·g⁻¹) incidentper unit time and unit area in a wavelength range of 700 nm or more and780 nm or less.

A second embodiment of the present disclosure is a plant cultivationmethod including irradiating plants with light from the light emittingdevice.

According to embodiments of the present disclosure, a light emittingdevice capable of promoting growth of plants and a plant cultivationmethod can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross sectional view of a light emitting deviceaccording to an embodiment of the present disclosure.

FIG. 2 is a diagram showing spectra of wavelengths and relative photonflux densities of exemplary light emitting devices according toembodiments of the present disclosure and a comparative light emittingdevices.

FIG. 3 is a graph showing fresh weight (edible part) at the harvest timeof each plant grown by irradiating the plant with light from exemplarylight emitting devices according to embodiments of the presentdisclosure and a comparative light emitting device.

FIG. 4 is a graph showing nitrate nitrogen content in each plant grownby irradiating the plant with light from exemplary light emittingdevices according to embodiments of the present disclosure and acomparative light emitting device.

DETAILED DESCRIPTION

A light emitting device and a plant cultivation method according to thepresent invention will be described below based on an embodiment.However, the embodiment described below only exemplifies the technicalconcept of the present invention, and the present invention is notlimited to the light emitting device and plant cultivation methoddescribed below. In the present specification, the relationship betweenthe color name and the chromaticity coordinate, the relationship betweenthe wavelength range of light and the color name of monochromatic lightfollows JIS Z8110.

Light Emitting Device

An embodiment of the present disclosure is a light emitting deviceincluding a light emitting element having a light emission peakwavelength in a range of 380 nm or more and 490 nm or less (hereinaftersometimes referred to as a “region of from near ultraviolet to bluecolor”), and a first fluorescent material emitting light having at leastone light emission peak wavelength in a range of 580 nm or more and lessthan 680 nm by being excited by light from the light emitting element.The light emitting device emits light having a ratio R/B of a photonflux density R to a photon flux density B within a range of 2.0 or moreand 4.0 or less, and a ratio R/FR of the photon flux density R to aphoton flux density FR within a range of 0.7 or more and 13.0 or less,where the photon flux density R is the number of light quanta(μmol·m⁻²·g⁻¹) incident per unit time and unit area in a wavelengthrange of 620 nm or more and less than 700 nm, the photon flux density Bis the number of light quanta (μmol·m⁻²·g⁻¹) incident per unit time andunit area in a wavelength range of 380 nm or more and 490 nm or less,and the photon flux density FR is the number of light quanta(μmol·m⁻²·g⁻¹) incident per unit time and unit area in a wavelengthrange of 700 nm or more and 780 nm or less.

An example of the light emitting device according to one embodiment ofthe present disclosure is described below based on the drawings. FIG. 1is a schematic cross sectional view showing a light emitting device 100according to an embodiment of the present disclosure.

The light emitting device 100 includes a molded article 40, a lightemitting element 10 and a fluorescent member 50, as shown in FIG. 1. Themolded article 40 includes a first lead 20 and a second lead 30 that areintegrally molded with a resin portion 42 containing a thermoplasticresin or a thermosetting resin. The molded article 40 forms a depressionhaving a bottom and sides, and the light emitting element 10 is placedon the bottom of the depression. The light emitting element 10 has apair of an anode and a cathode, and the anode and the cathode areelectrically connected to the first lead 20 and the second lead 30respectively through the respective wires 60. The light emitting element10 is covered with the fluorescent member 50. The fluorescent member 50includes, for example, a fluorescent material 70 performing wavelengthconversion of light from the light emitting element 10, and a resin. Thefluorescent material 70 includes a first fluorescent material 71 and asecond fluorescent material 72. A part of the first lead 20 and thesecond lead 30 that are connected to a pair of the anode and the cathodeof the light emitting element 10 is exposed toward outside a packageconstituting the light emitting element 100. The light emitting device100 can emit light by receiving electric power supply from the outsidethrough the first lead 20 and the second lead 30.

The fluorescent member 50 not only performs wavelength conversion oflight emitted from the light emitting element 10, but functions as amember for protecting the light emitting element 10 from the externalenvironment. In FIG. 1, the fluorescent material 70 is localized in thefluorescent member 50 in the state that the first fluorescent material71 and the second fluorescent material 72 are mixed with each other, andis arranged adjacent to the light emitting element 10. This constitutioncan efficiently perform the wavelength conversion of light from thelight emitting element 10 in the fluorescent material 70, and as aresult, can provide a light emitting device having excellent lightemission efficiency. The arrangement of the fluorescent member 50containing the fluorescent material 70, and the light emitting element10 is not limited to the embodiment that the fluorescent material 70 isarranged adjacent to the light emitting element 10 as shown in FIG. 1,and considering the influence of heat generated from the light emittingelement 10, the fluorescent material 70 can be arranged separated fromthe light emitting element 10 in the fluorescent member 50. Furthermore,light having suppressed color unevenness can be emitted from the lightemitting device 100 by arranging the fluorescent material 70 almostevenly in the fluorescent member 50. In FIG. 1, the fluorescent material70 is arranged in the state that the first fluorescent material 71 andthe second fluorescent material 72 are mixed with each other. However,for example, the first fluorescent material 71 may be arranged in alayer state and the second fluorescent material 72 may be arrangedthereon in another layer state. Alternatively, the second fluorescentmaterial 72 may be arranged in a layer state and the first fluorescentmaterial 71 may be arranged thereon in another layer state.

The light emitting device 100 includes the first fluorescent material 71having at least one light emission peak wavelength in a range of 580 nmor more and less than 680 nm by being excited by light from the lightemitting element 10, and preferably further includes the secondfluorescent material 72 having at least one light emission peakwavelength in a range of 680 nm or more and 800 nm or less by beingexcited by light from the light emitting element 10.

The first fluorescent material 71 and the second fluorescent material 72are contained in, for example, the fluorescent member 50 covering thelight emitting element 10. The light emitting device 100 in which thelight emitting element 10 has been covered with the fluorescent member50 containing the first fluorescent material 71 and the secondfluorescent material 72 emits light having at least one light emissionpeak wavelength in a range of 580 nm or more and less than 680 nm by apart of light emission of the light emitting element 10 that is absorbedin the first fluorescent material 71. Furthermore, the light emittingdevice 100 emits light having at least one light emission peakwavelength in a range of 680 nm or more and 800 nm or less by a part oflight emission of the light emitting element 10 that is absorbed in thesecond fluorescent material 72.

Plants grow when a pigment (chlorophyll a and chlorophyll b) present inchlorophyll thereof absorbs light and additionally takes carbon dioxidegas and water therein, and these are converted to carbohydrates(saccharides) by photosynthesis. Chlorophyll a and chlorophyll b used ingrowth promotion of plants particularly have absorption peaks in a redregion of 625 nm or more and 675 nm or less and a blue region of 425 nmor more and 475 nm or less. The action of photosynthesis by chlorophyllsof plants mainly occurs in a wavelength range of 400 nm or more and 700nm or less, but chlorophyll a and chlorophyll b further have localabsorption peaks in a region of 700 nm or more and 800 nm or less.

For example, when plants are irradiated with light having longerwavelength than and absorption peak (in the vicinity of 680 nm) in a redregion of chlorophyll a, a phenomenon called red drop, in which activityof photosynthesis rapidly decreases, occurs. However, it is known thatwhen plants are irradiated with light containing near infrared regiontogether with light of red region, photosynthesis is accelerated by asynergistic effect of those two kinds of lights. This phenomenon iscalled the Emerson effect.

Intensity of light with which plants are irradiated is represented byphoton flux density. The photon flux density (μmol·m⁻²·s⁻¹) is thenumber of photons reaching a unit area per unit time. The amount ofphotosynthesis depends on the number of photons, and therefore does notdepend on other optical characteristics if the photon flux density isthe same. However, wavelength dependency activating photosynthesisdiffers depending on photosynthetic pigment. Intensity of lightnecessary for photosynthesis of plants is sometimes represented byPhotosynthetic Photon Flux Density (PPFD).

The light emitting device 100 emits light having a ratio R/B of a photonflux density R to a photon flux density B within a range of 2.0 or moreand 4.0 or less, and a ratio R/FR of the photon flux density R to aphoton flux density FR within a range of 0.7 or more and 13.0 or less,where the photon flux density R is the number of light quanta(μmol·m⁻²·g⁻¹) incident per unit time and unit area in a wavelengthrange of 620 nm or more and less than 700 nm, the photon flux density Bis the number of light quanta (μmol·m⁻²·g⁻¹) incident per unit time andunit area in a wavelength range of 380 nm or more and 490 nm or less,and the photon flux density FR is the number of light quanta(μmol·m⁻²·g⁻¹) incident per unit time and unit area in a wavelengthrange of 700 nm or more and 780 nm or less.

It is estimated that in plants, which are irradiated with lightcontaining the photon flux density FR from the light emitting device100, photosynthesis is activated by Emerson effect, and as a result,growth of plants can be promoted. Furthermore, when plants areirradiated with light containing the photon flux density FR, growth ofthe plants can be promoted by a reversible reaction between red lightirradiation, to which chlorophyll as chromoprotein contained in plantshas participated, and far infrared light irradiation.

Examples of nutrients necessary for growth of plants include nitrogen,phosphoric acid, and potassium. Of those nutrients, nitrogen is absorbedin plants as nitrate nitrogen (nitrate ion: NO₃). The nitrate nitrogenchanges into nitrite ion (NO₂) by a reduction reaction, and when thenitrite ion is further reacted with fatty acid amine, nitrosoamine isformed. It is known that nitrite ion acts to hemoglobin in blood, and itis known that a nitroso compound sometimes affects health of a humanbody. Mechanism of converting nitrate nitrogen into nitrite ion in vivois complicated, and the relationship between the amount of intake ofnitrate nitrogen and the influence to health of a human body is notclarified. However, it is desired that the content of nitrate nitrogenhaving a possibility of affecting health of a human body is smaller.

For the above reasons, nitrogen is one of nutrients necessary for growthof plants, but it is preferred that the content of nitrate nitrogen infood plants be reduced to a range that does not disturb the growth ofplants.

It is preferred that the light emitting device 100 further include thesecond fluorescent material 72 having at least one light emission peakwavelength in a range of 680 nm or more and 800 nm or less by beingexcited by light from the light emitting element 10, wherein the R/FRratio is within a range of 0.7 or more and 5.0 or less. The R/FR ratiois more preferably within a range of 0.7 or more and 2.0 or less.

Light Emitting Element

The light emitting element 10 is used as an excitation light source, andis a light emitting element emitting light having a light emission peakwavelength in a range of 380 nm or more and 490 nm or less. As a result,a stable light emitting device having high efficiency, high linearity ofoutput to input and strong mechanical impacts can be obtained.

The range of the light emission peak wavelength of the light emittingelement 10 is preferably in a range of 390 nm or more and 480 nm orless, more preferably in a range of 420 nm or more and 470 nm or less,and still more preferably in a range of 440 nm or more and 460 nm orless, and particularly preferably in a range of 445 nm or more and 455nm or less. A light emitting element including a nitride semiconductor(In_(x)Al_(y)Ga_(1-x-y)N, 0≤X, 0≤Y and X+Y≤1) is preferably used as thelight emitting element 10.

The half value width of emission spectrum of the light emitting element10 can be, for example, 30 nm or less.

Fluorescent Member

The fluorescent member 50 used in the light emitting device 100preferably includes the first fluorescent material 71 and a sealingmaterial, and more preferably further includes the second fluorescentmaterial 72. A thermoplastic resin and a thermosetting resin can be usedas the sealing material. The fluorescent member 50 may contain othercomponents such as a filler, a light stabilizer and a colorant, inaddition to the fluorescent material and the sealing material. Examplesof the filler include silica, barium titanate, titanium oxide andaluminum oxide.

The content of other components other than the fluorescent material 70and the sealing material in the fluorescent member 50 is preferably in arange of 0.01 parts by mass or more and 20 parts by mass or less, per100 parts by mass of the sealing material.

The total content of the fluorescent material 70 in the fluorescentmember 50 can be, for example, 5 parts by mass or more and 300 parts bymass or less, per 100 parts by mass of the sealing material. The totalcontent is preferably 10 parts by mass or more and 250 parts by mass orless, more preferably 15 parts by mass or more and 230 parts by mass orless, and still more preferably 15 parts by mass or more and 200 partsby mass or less. When the total content of the fluorescent material 70in the fluorescent member 50 is within the above range, the lightemitted from the light emitting element 10 can be efficiently subjectedto wavelength conversion in the fluorescent material 70.

First Fluorescent Material

The first fluorescent material 71 is a fluorescent material that isexcited by light from the light emitting element 10 and emits lighthaving at least one light emission peak wavelength in a range of 580 nmor more and less than 680 nm. Examples of the first fluorescent material71 include an Mn⁴⁺-activated fluorogermanate fluorescent material, anEu²⁺-activated nitride fluorescent material, an Eu²⁺-activated alkalineearth sulfide fluorescent material and an Mn⁴⁺-activated halidefluorescent material. The first fluorescent material 71 may use oneselected from those fluorescent materials and may use a combination oftwo or more thereof. The first fluorescent material preferably containsan Eu²⁺-activated nitride fluorescent material and an Mn⁴⁺-activatedfluorogermanate fluorescent material.

The Eu²⁺-activated nitride fluorescent material is preferably afluorescent material that has a composition including at least oneelement selected from Sr and Ca, and Al and contains silicon nitridethat is activated by Eu²⁺, or a fluorescent material that has acomposition including at least one element selected from the groupconsisting of alkaline earth metal elements and at least one elementselected from the group consisting of alkali metal elements and containsaluminum nitride that is activated by Eu²⁺.

The halide fluorescent material that is activated by Mn⁴⁺ is preferablya fluorescent material that has a composition including at least oneelement or ion selected from the group consisting of alkali metalelements and an ammonium ion (NH⁴⁺) and at least one element selectedfrom the group consisting of Group 4 elements and Group 14 elements andcontains a fluoride that is activated by Mn⁴⁺.

Examples of the first fluorescent material 71 specifically includefluorescent materials having any one composition of the followingformulae (I) to (VI).

(i−j) MgO.(j/2)Sc₂O₃.kMgF₂.mCaF₂.(1−n)GeO₂.(n/2)M^(t) ₂O₃:zMn⁴⁺  (I)

wherein M^(t) is at least one selected from the group consisting of Al,Ga, and In, and j, k, m, n, and z are numbers satisfying 2≤i≤4, 0≤j<0.5,0<k<1.5, 0≤m<1.5, 0<n<0.5, and 0<z<0.05, respectively.

(Ca_(1-p-q)Sr_(p)Eu_(q))AlSiN₃   (II)

wherein p and q are numbers satisfying 0≤p≤1.0, 0<q<1.0, and p+q<1.0.

M^(a) _(v)M^(b) _(w)M^(c) _(f)Al_(3-g)Si_(g)N_(h)   (III)

wherein M^(a) is at least one element selected from the group consistingof Ca, Sr, Ba, and Mg, M^(b) is at least one element selected from thegroup consisting of Li, Na, and K, M^(c) is at least one elementselected from the group consisting of Eu, Ce, Tb, and Mn, v, w, f, g,and h are numbers satisfying 0.80≤v≤1.05, 0.80≤w≤1.05, 0.001<f≤0.1,0≤g≤0.5, and 3.0≤h≤5.0, respectively.

(Ca_(1-r-s-t)Sr_(r)Ba_(s)Eu_(t))₂Si₅N₈   (IV)

wherein r, s, and t are numbers satisfying 0≤r≤1.0, 0≤s≤1.0, 0<t<1.0,and r+s+t≤1.0.

(Ca, Sr)S:Eu   (V)

A₂[M¹ _(1-u)Mn⁴⁺ _(u)F₆]  (VI)

wherein A is at least one selected from the group consisting of K, Li,Na, Rb, Cs, and NH₄ ₊ , M¹ is at least one element selected from thegroup consisting of Group 4 elements and Group 14 elements, and u is thenumber satisfying 0<u<0.2.

The content of the first fluorescent material 71 in the fluorescentmember 50 is not particularly limited as long as the R/B ratio is withina range of 2.0 or more and 4.0 or less. The content of the firstfluorescent material 71 in the fluorescent member 50 is, for example, 1part by mass or more, preferably 5 parts by mass or more, and morepreferably 8 parts by mass or more, per 100 parts by mass of the sealingmaterial, and is preferably 200 parts by mass or less, more preferably150 parts by mass or less, and still more preferably 100 parts by massor less, per 100 parts by mass of the sealing material. When the contentof the first fluorescent material 71 in the fluorescent member 50 iswithin the aforementioned range, the light emitted from the lightemitting element 10 can be efficiently subjected to wavelengthconversion, and light capable of promoting growth of plant can beemitted from the light emitting device 100.

The first fluorescent material 71 preferably contains at least twofluorescent materials, and in the case of containing at least twofluorescent materials, the first fluorescent material preferablycontains a fluorogermanate fluorescent material that is activated byMn⁴⁺ (hereinafter referred to as “MGF fluorescent material”), and afluorescent material that has a composition including at least oneelement selected from Sr and Ca, and Al, and contains silicon nitridethat is activated by Eu²⁺ (hereinafter referred to as “CASN fluorescentmaterial”).

In the case where the first fluorescent material 71 contains at leasttwo fluorescent materials and two fluorescent materials are a MGFfluorescent material and a CASN fluorescent material, where acompounding ratio thereof (MGF fluorescent material:CASN fluorescentmaterial) is preferably in a range of 50:50 or more and 99:1 or less,more preferably in a range of 60:40 or more and 97:3 or less, and stillmore preferably in a range of 70:30 or more and 96:4 or less, in massratio. In the case where the first fluorescent material contains twofluorescent materials, when those fluorescent materials are a MGFfluorescent material and a CASN fluorescent material and the mass ratiothereof is within the aforementioned range, the light emitted from thelight emitting element 10 can be efficiently subjected to wavelengthconversion in the first fluorescent material 71. In addition, the R/Bratio can be adjusted to within a range of 2.0 or more and 4.0 or less,and the R/FR ratio is easy to be adjusted to within a range of 0.7 ormore and 13.0 or less.

Second Fluorescent Material

The second fluorescent material 72 is a fluorescent material that isexcited by the light from the light emitting element 10 and emits lighthaving at least one light emission peak wavelength in a range of 680 nmor more and 800 nm or less.

The second fluorescent material 72 used in the light emitting deviceaccording to one embodiment of the present disclosure is a fluorescentmaterial that contains a first element Ln containing at least oneelement selected from the group consisting of rare earth elementsexcluding Ce, a second element M containing at least one elementselected from the group consisting of Al, Ga, In, Ce, and Cr, and has acomposition of an aluminate fluorescent material. When a molar ratio ofthe second element M is taken as 5, it is preferred that a molar ratioof Ce be a product of a value of a parameter x and 3, and a molar ratioof Cr be a product of a value of a parameter y and 3, wherein the valueof the parameter x is in a range of exceeding 0.0002 and less than 0.50,and the value of the parameter y is in a range of exceeding 0.0001 andless than 0.05.

The second fluorescent material 72 is preferably a fluorescent materialhaving the composition represented by the following formula (1):

(Ln_(1-x-y)Ce_(x)Cr_(y))₃M₅O₁₂   (1)

wherein Ln is at least one rare earth element selected from the groupconsisting of rare earth elements excluding Ce, M is at least oneelement selected from the group consisting of Al, Ga, and In, and x andy are numbers satisfying 0.0002<x<0.50 and 0.0001<y<0.05, respectively.

In this case, the second fluorescent material 72 has a compositionconstituting a garnet structure, and therefore is tough against heat,light, and water, has an absorption peak wavelength of excitedabsorption spectrum in the vicinity of 420 nm or more and 470 nm orless, and sufficiently absorbs the light from the light emitting element10, thereby enhancing light emitting intensity of the second fluorescentmaterial 72, which is preferred. Furthermore, the second fluorescentmaterial 72 is excited by light having light emission peak wavelength ina range of 380 nm or more and 490 nm or less and emits light having atleast one light emission peak wavelength in a range of 680 nm or moreand 800 nm or less.

In the second fluorescent material 72, from the standpoint of stabilityof a crystal structure, Ln is preferably at least one rare earth elementselected from the group consisting of Y, Gd, Lu, La, Tb, and Pr, and Mis preferably Al or Ga.

In the second fluorescent material 72, the value of the parameter x ismore preferably in a range of 0.0005 or more and 0.400 or less(0.0005≤x≤0.400), and still more preferably in a range of 0.001 or moreand 0.350 or less (0.001≤x≤0.350).

In the second fluorescent material 72, the value of the parameter y ispreferably in a range of exceeding 0.0005 and less than 0.040(0.0005<y<0.040), and more preferably in a range of 0.001 or more and0.026 or less (0.001≤y≤0.026).

The parameter x is an activation amount of Ce and the value of theparameter x is in a range of exceeding 0.0002 and less than 0.50(0.0002<x<0.50), and the parameter y is an activation amount of Cr. Whenthe value of the parameter y is in a range of exceeding 0.0001 and lessthan 0.05 (0.0001<y<0.05), the activation amount of Ce and theactivation amount of Cr that are light emission centers contained in thecrystal structure of the fluorescent material are within optimum ranges,the decrease of light emission intensity due to the decrease of lightemission center can be suppressed, the decrease of light emissionintensity due to concentration quenching caused by the increase of theactivation amount can be suppressed, and light emission intensity can beenhanced.

Production Method of Second Fluorescent Material

A method for producing the second fluorescent material 72 includes thefollowing method.

A compound containing at least one rare earth element Ln selected fromthe group consisting of rare earth elements excluding Ce, a compoundcontaining at least one element M selected from the group consisting ofAl, Ga, and In, a compound containing Ce and a compound containing Crare mixed such that, when the total molar composition ratio of the M istaken as 5 as the standard, in the case where the total molarcomposition ratio of Ln, Ce, and Nd is 3, the molar ratio of Ce is aproduct of 3 and a value of a parameter x, and the molar ratio of Cr isa product of 3 and a value of a parameter y, the value of the parameterx is in a range of exceeding 0.0002 and less than 0.50 and the value ofthe parameter y is in a range of exceeding 0.0001 and less than 0.05,thereby obtaining a raw material mixture, the raw material mixture isheat-treated, followed by classification and the like, thereby obtainingthe second fluorescent material.

Compound Containing Rare Earth Element Ln

Examples of the compound containing rare earth element Ln includeoxides, hydroxides, nitrides, oxynitrides, fluorides, and chlorides,that contain at least one rare earth element Ln selected from the groupconsisting of rare earth elements excluding Ce. Those compounds may behydrates. At least a part of the compounds containing rare earth elementmay use a metal simple substance or an alloy containing rare earthelement. The compound containing rare earth element is preferably acompound containing at least one rare earth element Ln selected from thegroup consisting of Y, Gd, Lu, La, Tb, and Pr. The compound containingrare earth element may be used alone or may be used as a combination ofat least two compounds containing rare earth element.

The compound containing rare earth element is preferably an oxide thatdoes not contain elements other than the target composition, as comparedwith other materials. Examples of the oxide specifically include Y₂O₃,Gd₂O₃, Lu₂O₃, La₂O₃, Tb₄O₇ and Pr₆O₁₁.

Compound Containing M

Examples of the compound containing at least one element M selected fromthe group consisting of Al, Ga, and In include oxides, hydroxides,nitrides, oxynitrides, fluorides, and chlorides, that contain Al, Ga, orIn. Those compounds may be hydrates. Furthermore, Al metal simplesubstance, Ga metal simple substance, In metal simple substance, Alalloy, Ga alloy or In alloy may be used, and metal simple substance oran alloy may be used in place of at least a part of the compound. Thecompound containing Al, Ga, or In may be used alone or may be used as acombination of two or more thereof. The compound containing at least oneelement selected from the group consisting of Al, Ga, and In ispreferably an oxide. The reason for this is that an oxide that does notcontain elements other than the target composition, as compared withother materials, and a fluorescent material having a target compositionare easy to be obtained. When a compound containing elements other thanthe target composition has been used, residual impurity elements aresometimes present in the fluorescent material obtained. The residualimpurity element becomes a killer factor in light emission, leading tothe possibility of remarkable decrease of light emission intensity

Examples of the compound containing Al, Ga, or In specifically includeAl₂O₃, Ga₂O₃, and In₂O₃.

Compound Containing Ce and Compound Containing Cr

Examples of the compound containing Ce or the compound containing Crinclude oxides, hydroxides, nitrides, fluorides, and chlorides, thatcontain cerium (Ce) or chromium (Cr). Those compounds may be hydrates.Ce metal simple substance, Ce alloy, Cr metal simple substance, or Cralloy may be used, and a metal simple substance or an alloy may be usedin place of a part of the compound. The compound containing Ce or thecompound containing Cr may be used alone or may be used as a combinationof two or more thereof. The compound containing Ce or the compoundcontaining Cr is preferably an oxide. The reason for this is that anoxide that does not contain elements other than the target composition,as compared with other materials, and a fluorescent material having atarget composition are easy to be obtained. When a compound containingelements other than the target composition has been used, residualimpurity elements are sometimes present in the fluorescent materialobtained. The residual impurity element becomes a killer factor in lightemission, leading to the possibility of remarkable decrease of lightemission intensity.

Example of the compound containing Ce specifically includes CeO₂, andexample of the compound containing Cr specifically includes Cr₂O₃.

The raw material mixture may contain a flux such as a halide, asnecessary. When a flux is contained in the raw material mixture,reaction of raw materials with each other is accelerated, and a solidphase reaction is easy to proceed further uniformly. It is consideredthat a temperature for heat-treating the raw material mixture is almostthe same as a formation temperature of a liquid phase of a halide usedas a flux or is a temperature higher than the formation temperature,and, as a result, the reaction is accelerated.

Examples of the halide include fluorides, chlorides of rare earthmetals, alkali earth metals, and alkali metals. When a halide of rareearth metal is used as the flux, the flux can be added as a compound soas to achieve a target composition. Examples of the flux specificallyinclude BaF₂ and CaF₂. Of those, BaF₂ is preferably used. When bariumfluoride is used as the flux, a garnet crystal structure is stabilizedand a composition of a garnet crystal structure is easy to be formed.

When the raw material mixture contains a flux, the content of the fluxis preferably 20 mass % or less, and more preferably 10 mass % or less,and is preferably 0.1 mass % or more, on the basis of the raw materialmixture (100 mass %). When the flux content is within the aforementionedrange, the problem that it is difficult to form a garnet crystalstructure due to the insufficiency of particle growth by small amount ofthe flux is prevented, and furthermore, the problem that it is difficultto form a garnet crystal structure due to too large amount of the fluxis prevented.

The raw material mixture is prepared, for example, as follows. Each ofraw materials is weighed so as to be a compounding ratio. Thereafter,the raw materials are subjected to mixed grinding using a dry grindingmachine such as ball mill, are subjected to mixed grinding using amortar and a pestle, are subjected to mixing using a mixing machine suchas a ribbon blender, for example, or are subjected to mixed grindingusing both a dry grinding machine and a mixing machine. As necessary,the raw material mixture may be classified using a wet separator such asa setting tank generally used industrially, or a dry classifier such asa cyclone. The mixing may be conducted by dry mixing or may be conductedby wet mixing by adding a solvent. The mixing is preferably dry mixing.The reason for this is that dry mixing can shorten a processing time ascompared with wet drying, and this leads to the improvement ofproductivity.

The raw material mixture after mixing each raw material is dissolved inan acid, the resulting solution is co-precipitated in oxalic acid, aproduct formed by the co-precipitation is baked to obtain an oxide, andthe oxide may be used as the raw material mixture.

The raw material mixture can be heat-treated by placing it in acrucible, a boat made of a carbon material (such as graphite), boronnitride (BN), aluminum oxide (alumina), tungsten (W) or molybdenum (Mo).

From the standpoint of stability of a crystal structure, the temperaturefor heat-treating the raw material mixture is preferably in a range of1,000° C. or higher and 2,100° C. or lower, more preferably in a rangeof 1,100° C. or higher and 2,000° C. or lower, still more preferably ina range of 1,200° C. or higher and 1,900° C. or lower, and particularlypreferably in a range of 1,300° C. or higher and 1,800° C. or lower. Theheat treatment can use an electric furnace or a gas furnace.

The heat treatment time varies depending on a temperature rising rate, aheat treatment atmosphere. The heat treatment time after reaching theheat treatment temperature is preferably 1 hour or more, more preferably2 hours or more, and still more preferably 3 hours or more, and ispreferably 20 hours or less, more preferably 18 hours or less and stillmore preferably 15 hours or less.

The atmosphere for heat-treating the raw material mixture is an inertatmosphere such as argon or nitrogen, a reducing atmosphere containinghydrogen, or an oxidizing atmosphere such as the air. The raw materialmixture may be subjected to a two-stage heat treatment of a first heattreatment of heat-treating in the air or a weakly reducing atmospherefrom the standpoint of, for example, prevention of blackening, and asecond heat treatment of heat-treating in a reducing atmosphere from thestandpoint of enhancing absorption efficiency of light having a specificlight emission peak wavelength. The fluorescent material constituting agarnet structure is that reactivity of the raw material mixture isimproved in an atmosphere having high reducing power such as a reducingatmosphere. Therefore, the fluorescent material can be heat-treatedunder the atmospheric pressure without pressurizing. For example, theheat treatment can be conducted by the method disclosed in JapanesePatent Application No. 2014-260421.

The fluorescent material obtained may be subjected to post-treatmentsteps such as a solid-liquid separation by a method such as cleaning orfiltration, drying by a method such as vacuum drying, and classificationby dry sieving. After those post-treatment steps, a fluorescent materialhaving a desired average particle diameter is obtained.

Other Fluorescent Materials

The light emitting device 100 may contain other kinds of fluorescentmaterials, in addition to the first fluorescent material 71.

Examples of other kinds of fluorescent materials include a greenfluorescent material emitting green color by absorbing a part of thelight emitted from the light emitting element 10, a yellow fluorescentmaterial emitting yellow color, and a fluorescent material having alight emission peak wavelength in a wavelength range exceeding 680 nm.

Examples of the green fluorescent material specifically includefluorescent materials having any one of compositions represented by thefollowing formulae (i) to (iii).

M¹¹ ₈MgSi₄O₁₆X¹¹:Eu   (i)

wherein M¹¹ is at least one selected from the group consisting of Ca,Sr, Ba, and Zn, and X¹¹ is at least one selected from the groupconsisting of F, Cl, Br, and I.

Si_(6-b)Al_(b)O_(b)N_(8-b):Eu   (ii)

wherein b satisfies 0<b<4.2.

M¹³Ga₂S₄:Eu   (iii)

wherein M¹³ is at least one selected from the group consisting of Mg,Ca, Sr, and Ba.

Examples of the yellow fluorescent material specifically includefluorescent materials having any one of compositions represented by thefollowing formulae (iv) to (v).

M¹⁴ _(c/d)Si_(12-(c+d))Al_((c+d))O_(d)N_((16-d)):Eu   (iv)

wherein M¹⁴ is at least one selected from the group consisting of Sr,Ca, Li, and Y. A value of a parameter c is in a range of 0.5 to 5, avalue of a parameter d is in a range of 0 to 2.5, and the parameter d isan electrical charge of M¹⁴.

M¹⁵ ₃Al₅O₁₂:Ce   (v)

wherein M¹⁵ is at least one selected from the group consisting of Y andLu.

Examples of the fluorescent material having light emission peakwavelength in a wavelength range exceeding 680 nm specifically includefluorescent materials having any one of compositions represented by thefollowing formulae (vi) to (x).

Al₂O₃:Cr   (vi)

CaYAlO₄:Mn   (vii)

LiAlO₂:Fe   (viii)

CdS:Ag   (ix)

GdAlO₃:Cr   (x)

The light emitting device 100 can be utilized as a light emitting devicefor plant cultivation that can activate photosynthesis of plants andpromote growth of plants so as to have favorable form and weight.

Plant Cultivation Method

The plant cultivation method of one embodiment of the present disclosureis a method for cultivating plants, including irradiating plants withlight emitted from the light emitting device 100. In the plantcultivation method, plants can be irradiated with light from the lightemitting device 100 in plant factories that are completely isolated fromexternal environment and make it possible for artificial control. Thekind of plants is not particularly limited. However, the light emittingdevice 100 of one embodiment of the present disclosure can activatephotosynthesis of plants and promote growth of plants such that a stem,a leaf, a root, a fruit have favorable form and weight, and therefore ispreferably applied to cultivation of vegetables, flowers that containmuch chlorophyll performing photosynthesis. Examples of the vegetablesinclude lettuces such as garden lettuce, curl lettuce, Lamb's lettuce,Romaine lettuce, endive, Lollo Rosso, Rucola lettuce, and frill lettuce;Asteraceae vegetables such as “shungiku” (chrysanthemum coronarium);morning glory vegetables such as spinach; Rosaceae vegetables such asstrawberry; and flowers such as chrysanthemum, gerbera, rose, and tulip.

EXAMPLES

The present invention is further specifically described below byExamples and Comparative Examples.

Examples 1 to 5 First Fluorescent Material

Two fluorescent materials of fluorogarmanate fluorescent material thatis activated by Mn⁴⁺, having a light emission peak at 660 nm andfluorescent material containing silicon nitride that are activated byEu²⁺, having a light emission peak at 660 nm were used as the firstfluorescent material 71. In the first fluorescent material 71, a massratio of a MGF fluorescent material to a CASN fluorescent material(MGF:CASN) was 95:5.

Second Fluorescent Material

Fluorescent material that is obtained by the following production methodwas used as the second fluorescent material 72.

55.73 g of Y₂O₃ (Y₂O₃ content: 100 mass %), 0.78 g of CeO₂ (CeO₂content: 100 mass %), 0.54 g of Cr₂O₃ (Cr₂O₃ content: 100 mass %,) and42.95 g of Al₂O₃ (Al₂O₃ content: 100 mass %) were weighed as rawmaterials, and 5.00 g of BaF₂ as a flux was added to the mixture. Theresulting raw materials were dry mixed for 1 hour by a ball mill. Thus,a raw material mixture was obtained.

The raw material mixture obtained was placed in an alumina crucible, anda lid was put on the alumina crucible. The raw material mixture washeat-treated at 1,500° C. for 10 hours in a reducing atmosphere of H₂: 3vol % and N₂: 97 vol %. Thus, a calcined product was obtained. Thecalcined product was passed through a dry sieve to obtain a secondfluorescent material. The second fluorescent material obtained wassubjected to composition analysis by ICP-AES emission spectrometry usingan inductively coupled plasma emission analyzer (manufactured by PerkinElmer). The composition of the second fluorescent material obtained was(Y_(0.977)Ce_(0.009)Cr_(0.014))₃Al₅O₁₂ (hereinafter referred to as “YAG:Ce,Cr”).

Light Emitting Device

Nitride semiconductor having a light emission peak wavelength of 450 nmwas used as the light emitting element 10 in the light emitting device100.

Silicone resin was used as a sealing material constituting thefluorescent member 50, the first fluorescent material 71 and/or thesecond fluorescent material 72 was added to 100 parts by mass of thesilicone resin in the compounding ratio (parts by mass) shown in Table1, and 15 parts by mass of silica filler were further added thereto,followed by mixing and dispersing. The resulting mixture was degassed toobtain a resin composition constituting a fluorescent member. In each ofresin compositions of Examples 1 to 5, the compounding ratio of thefirst fluorescent material 71 and the second fluorescent material 72 wasadjusted as shown in Table 1, and those materials are compounded suchthat the R/B ratio is within a range of 2.0 or more and 2.4 or less, andthe R/FR ratio is within a range of 1.4 or more and 6.0 or less.

The resin composition was poured on the light emitting element 10 of adepressed portion of the molded article 40 to fill the depressedportion, and heated at 150° C. for 4 hours to cure the resincomposition, thereby forming the fluorescent member 50. Thus, the lightemitting device 100 as shown in FIG. 1 was produced in each of Examples1 to 5.

Comparative Example 1

A light emitting device X including a semiconductor light emittingelement having a light emission peak wavelength of 450 nm and a lightemitting device Y including a semiconductor light emitting elementhaving a light emission peak length of 660 nm were used, and the R/Bratio was adjusted to 2.5.

Evaluation Photon Flux Density

Photon flux densities of lights emitted from the light emitting device100 used in Examples 1 to 5 and the light emitting devices X and Y usedin Comparative Example 1 were measured using a photon measuring device(LI-250A, manufactured by Li-COR). The photon flux density B, the photonflux density R, and the photon flux density FR of lights emitted fromthe light emitting devices used in each of the Examples and ComparativeExample; the R/B ratio; and the R/FR ratio are shown in Table 1. FIG. 2shows spectra showing the relationship between a wavelength and arelative photon flux density, in the light emitting devices used in eachExample and Comparative Example.

Plant Cultivation Test

The plant cultivation method includes a method of conducting by “growthperiod by RGB light source (hereinafter referred to as a first growthperiod)” and “growth period by light source for plant growth(hereinafter referred to as a second growth period)” using a lightemitting device according to an embodiment of the present disclosure asa light source.

The first growth period uses RGB light source, and RGB type LEDgenerally known can be used as the RGB light source. The reason forirradiating plants with RGB type LED in the initial stage of the plantgrowth is that length of a stem and the number and size of true leavesin the initial stage of plant growth are made equal, thereby clarifyingthe influence by the difference of light quality in the second growthperiod.

The first growth period is preferably about 2 weeks. In the case wherethe first growth period is shorter than 2 weeks, it is necessary toconfirm that two true leaves develop and a root reaches length that cansurely absorb water in the second growth period. In the case where thefirst growth period exceeds 2 weeks, variation in the second growthperiod tends to increase. The variation is easy to be controlled by RGBlight source by which stem extension is inhibitory, rather than afluorescent lamp by which stem extension is easy to occur.

After completion of the first growth period, the second growth periodimmediately proceeds. It is preferred that plants are irradiated withlight emitted from a light emitting device according to an embodiment ofthe present disclosure. Photosynthesis of plants is activated byirradiating plants with light emitted from the light emitting deviceaccording to an embodiment of the present disclosure, and the growth ofplants can be promoted so as to have favorable form and weight.

The total growth period of the first growth period and the second growthperiod is about 4 to 6 weeks, and it is preferred that shippable plantscan be obtained within the period.

The cultivation test was specifically conducted by the following method.

Romaine lettuce (green romaine, produced by Nakahara Seed Co., Ltd.) wasused as cultivation plant.

First Growth Period

Urethane sponges (salad urethane, manufactured by M Hydroponic ResearchCo., Ltd.) having Romaine lettuce seeded therein were placed side byside on a plastic tray, and were irradiated with light from RGB-LEDlight source (manufactured by Shibasaki Inc.) to cultivate plants. Theplants were cultivated for 16 days under the conditions of roomtemperature: 22 to 23° C., humidity: 50 to 60%, photon flux density fromlight emitting device: 100 μmol·m⁻²·s⁻¹ and daytime hour: 16 hours/day.Only water was given until germination, and after the germination (about4 days later), a solution obtained by mixing Otsuka House #1(manufactured by Otsuka Chemical Co., Ltd.) and Otsuka House #2(manufactured by Otsuka Chemical Co., Ltd.) in a mass ratio of 3:2 anddissolving the mixture in water was used as a nutrient solution (OtsukaFormulation A). Conductivity of the nutrient was 1.5 ms·cm⁻¹.

Second Growth Period

After the first growth period, the plants were irradiated with lightfrom the light emitting devices of Examples 1 to 5 and ComparativeExample 1, and were subjected to hydroponics.

The plants were cultivated for 19 days under the conditions of roomtemperature: 22 to 24° C., humidity: 60 to 70%, CO₂ concentration: 600to 700 ppm, photon flux density from light emitting device: 125μmol·m⁻²·s⁻¹ and daytime hour: 16 hours/day. Otsuka Formulation A wasused as the nutrient solution. Conductivity of the nutrient was 1.5ms·cm⁻¹. The values of the R/B and R/FR ratios of light for plantirradiation from each light emitting device in the second growth periodare shown in Table 1.

Measurement of Fresh Weight (Edible Part)

The plants after cultivation were harvested, and wet weights of aterrestrial part and a root were measured. The wet weight of aterrestrial part of each of 6 cultivated plants having been subjected tohydroponics by irradiating with light from the light emitting devices ofExamples 1 to 5 and Comparative Example 1 was measured as a fresh weight(edible part) (g). The results obtained are shown in Table 1 and FIG. 3.

Measurement of Nitrate Nitrogen Content

The edible part (about 20 g) of each of the cultivated plants, fromwhich a foot about 5 cm had been removed, was frozen with liquidnitrogen and crushed with a juice mixer (laboratory mixer LM-PLUS,manufactured by Osaka Chemical Co., Ltd.) for 1 minute. The resultingliquid was filtered with Miracloth (manufactured by Milipore), and thefiltrate was centrifuged at 4° C. and 15,000 rpm for 5 minutes. Thenitrate nitrogen content (mg/100 g) in the cultivated plant in thesupernatant was measured using a portable reflection photometer system(product name: RQ flex system, manufactured by Merck) and a test paper(product name: Reflectoquant (registered trade mark), manufactured byKanto Chemical Co., Inc.). The results are shown in Table 1 and FIG. 4.

TABLE 1 Fluorescent material (parts by mass) Photon Ratio of Firstfluorescent Second fluorescent flux density photon flux Fresh weightNitrate nitrogen material material (μmol · m⁻² · s⁻¹) densities (Ediblepart) content (MGF/CASN = 95:5) (YAG:Ce,Cr) B R FR R/B R/FR (g) (mg/100g) Comparative — — 35.5 88.8 0.0 2.5 — 26.2 361.2 Example 1 Example 1 60— 31.5 74.9 12.6 2.4 6.0 35.4 430.8 Example 2 50 10 28.5 67.1 21.7 2.43.1 34.0 450.0 Example 3 40 20 25.8 62.0 28.7 2.4 2.2 33.8 452.4 Example4 30 30 26.8 54.7 33.5 2.0 1.6 33.8 345.0 Example 5 25 39 23.4 52.8 38.12.3 1.4 28.8 307.2

As shown in Table 1, for the light emitting devices in Examples 1 to 5,the R/B ratios are within a range of 2.0 or more and 4.0 or less and theR/FR ratios are within the range of 0.7 or more and 13.0 or less. ForRomaine lettuce cultivated by irradiating with light from the lightemitting device in Examples 1 to 5, the fresh weight (edible part) wasincreased as compared with Romaine lettuce cultivated by irradiatingwith light from the light emitting device used in Comparative Example 1.Therefore, cultivation of plants was promoted, as shown in Table 1 andFIG. 3.

As shown in FIG. 2, the light emitting device 100 in Example 1 had atleast one maximum value of the relative photon flux density in a rangeof 380 nm or more and 490 nm or less and in a range of 580 nm or moreand less than 680 nm. The light emitting devices 100 in Examples 2 to 5had at least one maximum value of relative photon flux density in arange of 380 nm or more and 490 nm or less, in a range of 580 nm or moreand less than 680 nm and in a range of 680 nm or more and 800 nm orless, respectively. The maximum value of the relative photon fluxdensity in a range of 380 nm or more and 490 nm or less is due to thelight emission of the light emitting element having light emission peakwavelength in a range of 380 nm or more and 490 nm or less, the maximumvalue of the relative photon flux density in a range of 580 nm or moreand less than 680 nm is due to the first fluorescent material emittingthe light having at least one light emission peak wavelength in a rangeof 580 nm or more and less than 680 nm, and the maximum value of therelative photon flux density in a range of 680 nm or more and 800 nm orless is due to the second fluorescent material emitting the light havingat least one light emission peak wavelength in a range of 680 nm or moreand 800 nm or less.

As shown in Table 1, for the light emitting devices 100 in Examples 4and 5, the R/B ratios are 2.0 and 2.3, respectively, and the R/FR ratiosare 1.6 and 1.4, respectively. The R/B ratios are within a range of 2.0or more and 4.0 or less, and the R/FR ratios are within a range of 0.7or more and 2.0 or less. For Romaine lettuces cultivated by irradiatingwith lights from the light emitting devices 100, the nitrate nitrogencontent is decreased as compared with Comparative Example 1. Plants, inwhich the nitrate nitrogen content having the possibility of adverselyaffecting health of human body had been reduced to a range that does notinhibit the cultivation of plants, could be cultivated, as shown inTable 1 and FIG. 4.

The light emitting device according to an embodiment of the presentdisclosure can be utilized as a light emitting device for plantcultivation that can activate photosynthesis and is capable of promotinggrowth of plants. Furthermore, the plant cultivation method, in whichplants are irradiated with the light emitted from the light emittingdevice according to an embodiment of the present disclosure, cancultivate plants that can be harvested in a relatively short period oftime and can be used in a plant factory.

Although the present disclosure has been described with reference toseveral exemplary embodiments, it shall be understood that the wordsthat have been used are words of description and illustration, ratherthan words of limitation. Changes may be made within the purview of theappended claims, as presently stated and as amended, without departingfrom the scope and spirit of the disclosure in its aspects. Although thedisclosure has been described with reference to particular examples,means, and embodiments, the disclosure may be not intended to be limitedto the particulars disclosed; rather the disclosure extends to allfunctionally equivalent structures, methods, and uses such as are withinthe scope of the appended claims.

One or more examples or embodiments of the disclosure may be referred toherein, individually and/or collectively, by the term “disclosure”merely for convenience and without intending to voluntarily limit thescope of this application to any particular disclosure or inventiveconcept. Moreover, although specific examples and embodiments have beenillustrated and described herein, it should be appreciated that anysubsequent arrangement designed to achieve the same or similar purposemay be substituted for the specific examples or embodiments shown. Thisdisclosure may be intended to cover any and all subsequent adaptationsor variations of various examples and embodiments. Combinations of theabove examples and embodiments, and other examples and embodiments notspecifically described herein, will be apparent to those of skill in theart upon reviewing the description.

In addition, in the foregoing Detailed Description, various features maybe grouped together or described in a single embodiment for the purposeof streamlining the disclosure. This disclosure may be not to beinterpreted as reflecting an intention that the claimed embodimentsrequire more features than are expressly recited in each claim. Rather,as the following claims reflect, inventive subject matter may bedirected to less than all of the features of any of the disclosedembodiments. Thus, the following claims are incorporated into theDetailed Description, with each claim standing on its own as definingseparately claimed subject matter.

The above disclosed subject matter shall be considered illustrative, andnot restrictive, and the appended claims are intended to cover all suchmodifications, enhancements, and other embodiments which fall within thetrue spirit and scope of the present disclosure. Thus, to the maximumextent allowed by law, the scope of the present disclosure may bedetermined by the broadest permissible interpretation of the followingclaims and their equivalents, and shall not be restricted or limited bythe foregoing detailed description.

What is claimed is:
 1. A fluorescent material, comprising: a first element Ln containing at least one element selected from the group consisting of rare earth elements excluding Ce, a second element M containing at least one element selected from the group consisting of Al, Ga, and In, Ce, and Cr, and having a composition of an aluminate fluorescent material, wherein a molar ratio of Ce is a product of a parameter x and 3, and a molar ratio of Cr is a product of a parameter y and 3, the parameter x is in a range of exceeding 0.0002 and less than 0.50, and the parameter y is in a range of exceeding 0.0001 and less than 0.05 when a molar ratio of the second element M is taken as 5 in the composition of the aluminate fluorescent material.
 2. The fluorescent material according to claim 1, wherein the first element Ln is at least one element selected from the group consisting of Y, Gd, Lu, La, Tb and Pr.
 3. The fluorescent material according to claim 1, wherein the second element M is Al or Ga.
 4. The fluorescent material according to claim 1, wherein the parameter x is in a range of 0.001 or more and 0.350 or less.
 5. The fluorescent material according to claim 1, wherein the parameter y is in a range of 0.001 or more and 0.026 or less.
 6. The fluorescent material according to claim 1, having a light emission peak wavelength in a range of 680 nm or more and 800 nm or less, as excited with light having a light emission peak wavelength in a range of 380 nm or more and 490 nm or less.
 7. The fluorescent material according to claim 1, having a composition represented by a following formula (1): (Ln_(1-x-y)Ce_(x)Cr_(y))₃M₅O₁₂   (1) wherein Ln is at least one element selected from the group consisting of rare earth elements excluding Ce, M is at least one element selected from the group consisting of Al, Ga, and In, and x and y satisfy 0.0002<x<0.50, and 0.0001<y<0.05.
 8. The fluorescent material according to claim 7, wherein Ln is at least one element selected from the group consisting of Y, Gd, Lu, La, Tb and Pr in the formula (1).
 9. The fluorescent material according to claim 7, wherein M is Al or Ga in the formula (1).
 10. The fluorescent material according to claim 7, wherein x satisfies 0.001≤x≤0.350 in the formula (1).
 11. The fluorescent material according to claim 7, wherein y satisfies 0.001≤y≤0.026 in the formula (1). 